So, does Michael Phelps believe in flossing?

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Reviving ancient remedies – Perfectly circular bruises are adorning the bodies of Olympians in Rio this summer -- particularly among swimmers such as Michel Phelps (pictured) -- after the sudden popularity of cupping, an ancient therapy practiced as far back at the 6th century. But this is one of many treatments used throughout history that aimed to control the flow of fluid within the body.

CNN spoke to Claudia Stein, professor of history at the University of Warwick, England, and Laurence Totelin, a historian of medicine at Cardiff University, Wales, to find out more about cupping and some of the more gruesome, but surprisingly commonplace, medical practices used to treat ailments throughout history.

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Cupping – Cupping therapy has been practiced from as early as the 6th century, according to Totelin, and is seeing a comeback today through the increased popularity of traditional medicine. "Globalization of medicine is attracting Western people to this holistic practice," says Stein.

The practice involves cups placed on specific regions of the body to create suction and encourage blood flow. Practitioners believe it promotes healing for a broad range of ailments in a similar way to the premise of bloodletting and leeching -- the goal being to balance levels of blood inside the body.

"Cupping was more common," says Totelin about the treatment which is still practiced today in Chinese medicine. In ancient times, however, its use was part of everyday life. "Cupping is one of the big things you do ... to be healthy," adds Stein. "[People would] place a cup to draw blood out of the body or to prevent getting sick."

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Bloodletting – Bloodletting is one of the oldest known medical practices and is thought to have begun with the ancient Egyptians. This ancient practice involved the drawing -- or letting -- of blood from the body, which was believed to balance an individual's fluid levels.

Many ancient therapies were based on the belief that the human body consisted of four fluids -- or humors -- blood, phlegm, black bile and yellow bile. If their levels were thought to be out of sync, a range of unpleasant treatments were used to restore them.

The procedure came with strict rules and restrictions, with cuts only being made at specific points on the body. "It was a very complicated practice," says Stein.

"You would bloodlet if you have too much blood," says Totelin. The symptoms of excessive blood varied between individuals and genders, with females thought to be imbalanced if their menstrual cycles were disrupted, or delayed, and males if they were low on energy and sluggish, Totelin explains.

However, bloodletting was also practiced regularly at specific times of year in order to simply stay healthy -- such as in the springtime, when blood was thought to be thinner, according to Stein. "[People] used bloodletting in certain seasons to give a fresh start into their year," she explains.

Among its key ingredients was oxgall (bile from a cow's stomach) -- perhaps not the nicest thing to rub in your eye, but far more pleasant than many of the grisly treatments from medicine's murky past.

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Leeches – These blood-sucking worms were used in a similar way to bloodletting but provided a more localized way of extracting excess blood from the body. "You put leeches on the blood to draw bad fluid," says Stein.

The animals have evolved for optimal blood extraction from humans and release hirudin -- an anticoagulant -- during feedings to enhance blood flow.

Their use can be traced back to ancient Indian Ayurveda practices and leeches are still sometimes used in modern medicine to restore circulation after surgery.

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Trepanation – Dating back before ancient Roman and Greek times, according to Totelin, holes were drilled into human skulls to relieve a range of ailments from migraines to head injuries.

The practice -- known as trepanation -- is considered by experts to be the oldest form of neurosurgery. Its original use was to relieve pressure, reduce swelling and also enhance overall bloodflow in the brain and improve well-being.

The premise behind the practice is still used by neurosurgeons today to reduce swelling and pressure in the brain before, or after, surgery.

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Mercury – For centuries, this poisonous chemical was taken in a range of forms -- pills, ointments, and inhalation. The one thing they all had in common was that they came with extensive, and long-lived, side effects including kidney failure, mouth ulcers and teeth loss. "We now know it was mercury poisoning," says Stein.

But the poison was considered an effective remedy, particularly against skin diseases. "Mercury was used for everything relating to skin diseases until the late 19th century," says Stein. It was also among the first treatments used against syphilis.

Mercury was believed to help people sweat and salivate, in line with the belief of restoring fluid levels inside the body to treat ailments. One treatment involved rubbing patients with mercury ointment and locking them in a secluded, stuffy room to promote sweating. "[It was] seen as a sign of the body healing itself by getting fluids out," says Stein.

Many people died from mercury poisoning, rather than the disease it was meant to cure. This 19th-century illustration shows "part of the face destroyed by [syphilis] and the baneful effects of mercury."

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Arsenic – From the 15th century onwards, people believed the body was made up of different elements which were needed in the right proportions. "If [they were] not, you used chemicals to put it in order," says Totelin. Those chemicals included lead, copper, silver and arsenic.

"Arsenic has always been a known poison," adds Stein, but its toxic properties did have some benefits. "It did kill bacteria but would not treat things long term," she says. In the 20th century arsenic was used in the first antibiotic treatment against syphilis, known as salvarsan, which was considered a magic bullet in the fight against the disease. It was a much needed alternative to pure mercury.

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Couching – Couching is considered one of the earliest forms of cataract surgery dating back to the 6th century and possibly back to the ancient Egyptians, according to Totelin.

Cataracts cause a clouding of the lens inside the eye -- resulting in blurred vision. In couching, pointed objects were used to dislodge the lens within the eye and push the clouded section towards the back of the eye. "People were often blind at an early age," says Totelin, whose research has discovered couching to have been a long-standing practice.

The treatment continues to be used in some forms of traditional medicine today as well as in rural areas, but doctors warn against its use, instead advocating cataract surgery -- used in current Western medical practices.

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Purging – Purging was a practice where poisonous plants were consumed to "rid the body of any superfluous liquids," according to Stein -- by inducing vomiting.

The aim was to empty the body of any of its contents which could be causing a person's ailments -- similar to the purging performed by cats and dogs.

"[There were] different plants you can give dependant on which area you live in," says Stein. A common plant consumed was hellebore -- also known then as the hell flower. Hellebore was also included in a range of ancient potions in ancient Greek and Japanese medicine. Its roots and stems were used to treat anything from melancholy and depression to coughs, epilepsy and dysentery.

This gallery was originally published in April 2016 and has been updated.

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Story highlights

Ford Vox: Michael Phelps, others using untraditional treatments like "cupping." And benefits of flossing now questioned

Vox: We know the mind has the capacity to palliate itself, so are cupping and flossing just features of a healthy imagination?

Ford Vox is a physician specializing in rehabilitation medicine and a journalist. He is a medical analyst for NPR station WABE-FM 90.1 in Atlanta. He writes frequently for CNN Opinion. Follow him on Twitter @FordVox. The opinions expressed in this commentary are solely those of the author.

(CNN)No, those purple spots viewers first noticed on Michael Phelps' back last weekend weren't telltale signs of Zika, or hickeys from the night before. As the media zoomed in, the world soon learned they were the result of a traditional Chinese technique called cupping, and as you might have heard by now, it's got quite a following among Olympic athletes.

As an American physician trained in the standard "allopathic" (that is, mainstream) regime, I'm inclined to roll my eyes. I'm skeptical, but open-minded enough to know not everything I do comes with a sterling base of, uh, evidence.

You see, all the Olympic excitement about cupping, which has me rubbing my chin, comes directly after a wave of news headlines calling into question another funny-looking health routine Westerners have dutifully performed since the early 1800s: flossing. Did these two treatments get to where they are in 2016, despite faults, due to valuable evidence or simple belief? We know the mind has the capacity to palliate itself, so are cupping and flossing just features of a healthy imagination?

Cupping is practiced outside the mainstream, but flossing is part of the American oral health pantheon, touted for years by the dentists and hygienists we've long thanked for setting our nation's smiles apart from others.

Photos:What a moment! These viral photos defined Rio 2016

South Korean gymnast Lee Eun-ju takes a selfie with North Korean gymnast Hong Un-jong during training on Thursday, August 4. Relations have been frosty between the North and South since its division following the end of World War II, but geopolitics were put to the side as the two Olympians came together.

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Photos:What a moment! These viral photos defined Rio 2016

Abbey D'Agostino of the United States leaves the track on a wheelchair after twisting her ankle in the 5000-meter semifinal on Tuesday, August 16. D'Agostino and New Zealand's Nikki Hamblin, right, collided during the race but helped each other up and managed to make it to the finish line.

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Photos:What a moment! These viral photos defined Rio 2016

Shaunae Miller of the Bahamas dives over the finish line to win gold in the 400 meters on Monday, August 15. She edged out American Allyson Felix by .07 seconds.

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Photos:What a moment! These viral photos defined Rio 2016

David Katoatau of Kiribati dances during the 105-kilogram (231-pound) weightlifting final on Monday, August 15. He finished sixth overall.

Jamaican sprinter Usain Bolt looks back at his competitors during a 100-meter semifinal on Sunday, August 14. Bolt won the final a short time later, becoming the first man in history to win the 100 meters at three straight Olympic Games.

The diving pool, right, is seen on Tuesday, August 9. The pool had turned from blue to green since Monday.

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Photos:What a moment! These viral photos defined Rio 2016

Rugby player Isadora Cerullo of Brazil, left, kisses Marjorie Enya, a volunteer at the Games, on Monday, August 8. Enya proposed to Cerullo after the rugby sevens match between Australia and New Zealand.

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Photos:What a moment! These viral photos defined Rio 2016

U.S. fencer Ibtihaj Muhammad celebrates after defeating Ukraine's Olena Kravatska in the individual sabre competition on Monday, August 8. Muhammad is the first U.S. Olympian to compete in hijab.

U.S swimmer Michael Phelps competes in the 4x100-meter freestyle relay on Sunday, August 7. The red marks on his body are the result of cupping -- an ancient therapy that has mostly been used in Middle Eastern and Asian countries, especially China.

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Photos:What a moment! These viral photos defined Rio 2016

U.S. swimmer Lilly King reacts after winning the 100-meter breaststroke semifinal on Sunday, August 7. King beat Russia's Yulia Efimova in both their semifinal and final faceoff after what had been billed as an Olympic grudge race.

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Photos:What a moment! These viral photos defined Rio 2016

Yusra Mardini, a swimmer for the Refugee Olympic team, competes in a 100-meter butterfly heat on Saturday, August 6. The Syrian native and her teammates have had a remarkable journey to the Games.

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Photos:What a moment! These viral photos defined Rio 2016

Silver medalist Yang Sun of China and gold medalist Mack Horton of Australia shake hands after the 400-meter swimming freestyle on Saturday, August 6. The Australian had opened up a war of words against his Chinese opponent in the buildup to the final, saying: "I don't have time or respect for drug cheats."

Yet now the Departments of Agriculture and Health and Human Services have dropped flossing from the country's dietary guidelines. The president of the American Academy of Periodontology actually admitted to a reporter that the scientific evidence is "weak" and studies examining flossing are inadequate.

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It's enough to make a doctor dizzy.

Let's look a little closer at the moving ground beneath us. Cupping is not the only untraditional treatment US Olympic athletes are taking up in Rio. The wrestling team has a newfound appreciation for brainwave-synching sleep music, according to Coach Matt Lindland. He thinks the Brain.fm app (artificial-intelligence-generated tunes for "focus, relaxation, meditation, naps and sleep") is giving his athletes an edge as they accomplish their power lifts.

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STAT News's Sharon Begley notes that the product's core claim, that its music syncs with your brain's own waves, is tough to believe when everyone's EEG is unique at any given time, and the app does no processing and matching of music to your EEG pattern.

Wacky? Maybe not entirely, when you consider that elite level athleticism is as much a mind game as a physical game -- and athletes will do just about anything (sexual abstinence, lucky underwear) to get into the zone. There's also plenty of medical evidence that one's attitude and outlook can make quite a difference in one's performance.

For example, when we ask people soon after an injury how long they think symptoms will last, people who think their symptoms will linger do indeed have more persistent symptoms compared with those who expect they'll recover quickly.

What about cupping, a therapy that has been around for 2,000 years and is mostly associated with traditional Chinese medicine? It's a simple enough physical process: Cups are heated with a flame, typically from burning off an alcohol coating, and then the cups are placed, opening-down, on the body part(s) that needs treatment. As the cup and the air within cool off, a resulting vacuum pulls up the skin, soft tissue, and even the muscle underneath. A new-wave version many Olympic athletes are using involves a mechanical suction pump, so no heat is involved.

Why might this relieve pain and help sports injuries heal? We know the suction force is great enough to break small capillaries in the skin, which causes the bruising, and this trauma to the soft tissue generates more local blood flow, bringing with it immune-system-signaling molecules that can kick off repair processes. I suspect simple distraction from pain is a major factor.

There have been hundreds of studies on cupping in the past decade, but much of the research finds a home in alternative medicine journals that aren't too popular among medical doctors.

Cupping did find its way into the American Pain Society's Journal of Pain in 2009, however, where it demonstrated superiority in a randomized trial to a sham treatment people would expect to work: heat. Subjects in that German study, who all had carpal tunnel syndrome, either got "wet cupping" (the above-described dry cupping but also pricking the skin with a lancet to provoke bleeding) or a heating pad. The group who got cupping reported less pain and more function than those who just got heat.

But a suction cup that leaves a dramatic circular bruise (and causes bleeding) should make a bigger psychological impact than a simple heating pad. One can see lasting evidence of the treatment with one's own eyes. That's a bigger placebo.

Another study addressed that problem by comparing dry cupping to a cup with a tiny air leak so it couldn't form a proper suction. Both cups relieved fibromyalgia pain better than "usual care," with no significant difference between them.

Think about that: People who got the leaky cup experienced no possible physiological change whatsoever from the actual cupping. There's no tugging at the skin, no broken capillaries, no change in circulation, and yet they felt better. They had one aspect in common with the real cupping group, though. Both groups, whether they knew it or not, were in the grips of positive thinking.

But even as I give the Olympic hopefuls a hard a time for their cupping and brain music, the news about flossing sets me back.

If you didn't see the headlines, a wily AP reporter, tipped off by his son's orthodontist, started asking dentists, periodontists and the US government thorny questions about flossing. Turns out there have not been rigorous randomized controlled trials to back up the commonly made claims that the practice helps prevent gum disease and cavities.

This has been openly discussed in dental journals, but much of the general public didn't know dentists don't have too much to go on beyond their clinical experiences when they're telling you you better floss.

But it's quite difficult to study flossing properly: You'd have to get a large group of people to avoid flossing for many years, enough time so that cavities and gingivitis can gradually develop, and compare their disease rate to another group that flosses religiously.

And the group that doesn't floss would have to brush their teeth for the same amount of time, and in the same way, using the similar toothbrushes and toothpaste as the group that isn't flossing.

Photos:Rio Olympics: Day 5

Katie Ledecky is congratulated by her U.S. teammates Allison Schmitt, Leah Smith and Emily DiRado after swimming the anchor leg of the 4x200 freestyle on Wednesday, August 10. The gold medal is Ledecky's third of the Rio Games.

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Photos:Rio Olympics: Day 5

Gabriel Barbosa, top, hugs his Brazilian teammate Neymar after scoring the first goal in a 4-0 victory over Denmark. It was the first goal Brazil had scored in three matches.

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Photos:Rio Olympics: Day 5

Kyle Chalmers of Australia celebrates after winning gold in the 100-meter freestyle. He is the first Australian to win the event since Mike Wenden in 1968.

U.S. beach volleyball player Kerri Walsh Jennings dives for a ball during a qualifying match.

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Photos:Rio Olympics: Day 5

A fan watches archery under pouring rain in Rio de Janeiro.

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American cyclist Kristin Armstrong shows her gold medal to her son, Lucas, after winning the time trial for the third straight Olympics. Williams won the event a day before turning 43 years old. She was the oldest woman in the field by seven years.

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Photos:Rio Olympics: Day 5

Nijat Rahimov, a weightlifter from Kazakhstan, celebrates after setting a world-record clean and jerk during the 77-kilogram (170-pound) competition. Rahimov lifted 214 kilograms (471.8 pounds) on the way to winning gold.

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Photos:Rio Olympics: Day 5

Madeleine Samantha Bodo Essissima plays a shot for Cameroon during a volleyball match against Russia.

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Photos:Rio Olympics: Day 5

Chinese field hockey players wear protective face masks as they wait for a corner shot from the Netherlands.

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Photos:Rio Olympics: Day 5

Tunisian fencer Ines Boubakri, left, competes against Italy's Elisa Di Francisca during a semifinal bout in the individual foil competition. Di Francisca advanced to the final but lost to Russia's Inna Deriglazova.

Russian boxer Vladimir Nikitin is attended to following an injury suffered in a bantamweight bout.

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Photos:Rio Olympics: Day 5

U.S. swimmer Ryan Murphy competes in a preliminary race for the 200-meter backstroke. Murphy won gold in the 100-meter backstroke earlier this week.

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Photos:Rio Olympics: Day 5

The diving pool has been dark green since Monday, and now the water polo pool, left, is also starting to turn green. Rio organizers said the cause is likely due to algae and that water tests showed there were no health risks.

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Photos:Rio Olympics: Day 5

North Korean table tennis player Kim Song-i focuses on the ball during her semifinal match against Ding Ning of China. Ding advanced to the gold-medal match, which she won.

Oh, and the two groups need to be of very similar age, socioeconomic background, keep to similar diets and maintain a similar general health status. Good luck conducting this multimillion-dollar enterprise. Industry has no motivation to fund it, subjects have no desire to join such a study, and I'd be thoroughly disgusted if the National Institutes of Health, with all of the more pressing problems out there, spent a dime on it. The same goes for cupping.

I trust the dentists and their experience comparing the mouths of their patients who floss regularly to those who don't floss in their own clinics.

And while I think that flossing is more important to the health of far more people — that is, pretty much everyone -- than cupping is to an elite group of athletes, both are relatively low risk activities even if they're not doing everything that's claimed.

One thing, though: Cupping can cause burns, so maybe you're better off with a mechanical vacuum method if you're going to do it, and flossing can send bacteria into the bloodstream, so discuss it with your doctor if you're immunocompromised.